U.S. patent application number 15/037250 was filed with the patent office on 2016-10-06 for method for producing barium titanate powder.
The applicant listed for this patent is SAKAI CHEMICAL INDUSTRY CO., LTD.. Invention is credited to Yuji BABA, Yukihiro KUNIYOSHI, Shinji OGAMA, Kazumi YAMANAKA, Minoru YONEDA.
Application Number | 20160289082 15/037250 |
Document ID | / |
Family ID | 53179257 |
Filed Date | 2016-10-06 |
United States Patent
Application |
20160289082 |
Kind Code |
A1 |
YAMANAKA; Kazumi ; et
al. |
October 6, 2016 |
METHOD FOR PRODUCING BARIUM TITANATE POWDER
Abstract
The invention provides a method for producing barium titanate
powder comprising the steps of: adding an aqueous slurry of anatase
hydrous titanium oxide having a BET specific surface area in the
range of 200 m.sup.2/g to 400 m.sup.2/g and a half width of
diffraction peak of (101) plane in the range of 2.3.degree. to
5.0.degree. as measured by X-ray diffraction to an aqueous solution
of barium hydroxide while maintaining the aqueous solution of
barium hydroxide at a temperature in the range from 80.degree. C.
to the boiling point thereof under normal pressure to cause a
reaction of the barium hydroxide with the hydrous titanium oxide to
provide an aqueous slurry of barium titanate precursor; and
subjecting the barium titanate precursor thus obtained to
hydrothermal treatment over a period of not less than 24 hours to
provide barium titanate particles.
Inventors: |
YAMANAKA; Kazumi;
(Sakai-shi, Osaka, JP) ; BABA; Yuji; (Sakai-shi,
Osaka, JP) ; YONEDA; Minoru; (Sakai-shi, Osaka,
JP) ; KUNIYOSHI; Yukihiro; (Iwaki-shi, Fukushima,
JP) ; OGAMA; Shinji; (Sakai-shi, Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAKAI CHEMICAL INDUSTRY CO., LTD. |
Osaka |
|
JP |
|
|
Family ID: |
53179257 |
Appl. No.: |
15/037250 |
Filed: |
August 22, 2014 |
PCT Filed: |
August 22, 2014 |
PCT NO: |
PCT/JP2014/071962 |
371 Date: |
May 17, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G 4/1227 20130101;
H01G 4/12 20130101; C01P 2002/72 20130101; C01G 23/006 20130101;
H01G 4/30 20130101; C01P 2006/12 20130101 |
International
Class: |
C01G 23/00 20060101
C01G023/00; H01G 4/12 20060101 H01G004/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2013 |
JP |
2013-238654 |
Claims
1. A method for producing barium titanate powder comprising the
steps of: adding an aqueous slurry of anatase hydrous titanium
oxide having a BET specific surface area in the range of 200
m.sup.2/g to 400 m.sup.2/g and a half width of diffraction peak of
(101) plane in the range of 2.3.degree. to 5.0.degree. as measured
by X-ray diffraction to an aqueous solution of barium hydroxide
while maintaining the aqueous solution of barium hydroxide at a
temperature in the range from 80.degree. C. to the boiling point
thereof under normal pressure to cause a reaction of the barium
hydroxide with the hydrous titanium oxide to provide an aqueous
slurry of barium titanate precursor; and subjecting the barium
titanate precursor thus obtained to hydrothermal treatment over a
period of not less than 24 hours to provide barium titanate
particles.
2. The method according to claim 1, wherein in the step of
subjecting the barium titanate precursor to hydrothermal treatment
to provide barium titanate, the hydrothermal treatment is performed
at a temperature of 250.degree. C. or less.
3. The method according to claim 1 comprising the steps of: adding
an aqueous solution of titanium tetrachloride and an aqueous
solution of an alkali to water maintained at a temperature of
45.degree. C. to 65.degree. C. at the same time while maintaining
the temperature of the resulting reaction mixture in the range of
45.degree. C. to 65.degree. C. and maintaining the pH thereof in
the range of 1.5 to 3.5 to simultaneously neutralize the titanium
tetrachloride with the alkali thereby to provide an aqueous slurry
of anatase hydrous titanium oxide having a BET specific surface
area in the range of 200 m.sup.2/g to 400 m.sup.2/g and a half
width of diffraction peak of (101) plane in the range of
2.3.degree. to 5.0.degree. as measured by X-ray diffraction; adding
the aqueous slurry of anatase hydrous titanium oxide thus obtained
to an aqueous solution of barium hydroxide while maintaining the
aqueous solution of barium hydroxide solution at a temperature in
the range from 80.degree. C. to the boiling point thereof under
normal pressure to cause a reaction of the barium hydroxide with
the hydrous titanium oxide to provide an aqueous slurry of barium
titanate precursor; and subjecting the barium titanate precursor
thus obtained to hydrothermal treatment over a period of not less
than 24 hours to provide barium titanate particles.
4. The method according to claim 3, wherein in the step of
subjecting the barium titanate precursor to hydrothermal treatment
to obtain barium titanate, the hydrothermal treatment is performed
at a temperature of 250.degree. C. or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing
barium titanate powder, more specifically to a method for producing
barium titanate powder which is comprised of uniform fine
particles, high in tetragonality, and superior in
dispersibility.
BACKGROUND ART
[0002] In recent years, a substantial improvement of the properties
of elements configuring the electronic devices and the starting
materials for manufacturing the electronic devices has been
strongly demanded with a reduction in size, an enhancement of
performance, and a reduction in weight of various electronic
devices.
[0003] For example, a multilayer ceramic capacitor (MLCC) has been
increasingly strongly demanded to reduce the layer thickness.
Therefore, barium titanate for use in dielectric layers in the MLCC
has been increasingly demanded to be uniform fine particles and to
be high in tetragonality and to be superior in dispersibility, for
example.
[0004] Heretofore, as a method for producing barium titanate, a
solid phase method, an oxalic acid method, a sol-gel method, and
the like are known. However, in order to produce barium titanate
fine particles, particularly those having a particle diameter of
about 250 nm or less, preferably about 150 nm or less, for
satisfying the recent demand for the reduction in layer thickness
of the MLCC, a hydrothermal process which is a wet process is
advantageous. Since the solid phase method and the oxalic acid
method include a calcination process, uniform particles are
difficult to obtain, and moreover the resulting particles are easy
to aggregate so that fine particles are difficult to obtain. The
sol-gel method employs an expensive alkoxide as the raw material,
and therefore the sol-gel method has a problem in the production
cost.
[0005] Various methods for producing barium titanate by the
hydrothermal process are heretofore already known. By way of
example, a method is mentioned in which an aqueous solution of
barium salt is added to and reacted with a slurry of hydrous
titanium oxide in the presence of a carboxylic acid to produce
barium titanate core particles, the slurry containing the barium
titanate core particles thus obtained is subjected to hydrothermal
treatment to obtain spherical barium titanate particles, and then
the obtained spherical barium titanate particles are calcined at a
temperature of 800.degree. C. to 1200.degree. C. (Patent Literature
1).
[0006] According to this method, barium titanate fine particles
having a relatively large BET specific surface area and a high
tetragonality can be obtained. However, as the method requires
calcination of barium titanate core particles, it is difficult to
obtain particles having a uniform particle diameter. It is also
difficult to obtain particles of fine particles because of
aggregation of particles. The use of such barium titanate as a
dielectric material in the manufacturing of MLCC poses difficulty
in satisfying the demand of reducing the layer thickness of
MLCC.
CITATION LIST
Patent Literature
Patent Literature 1: JP 2002-211926A
SUMMARY OF INVENTION
Technical Problem
[0007] The invention has been completed in order to solve the
above-mentioned problems involved in the production of barium
titanate powder. It is an object of the invention to provide a
method for producing barium titanate powder which is comprised of
uniform fine particles high in tetragonality and superior in
dispersibility.
Solution to Problem
[0008] The invention provides a method for producing barium
titanate powder comprising the steps of:
[0009] adding an aqueous slurry of anatase hydrous titanium oxide
having a BET specific surface area in the range of 200 m.sup.2/g to
400 m.sup.2/g and a half width of diffraction peak of (101) plane
in the range of 2.3.degree. to 5.0.degree. as measured by X-ray
diffraction to an aqueous solution of barium hydroxide while
maintaining the aqueous solution of barium hydroxide at a
temperature in the range from 80.degree. C. to the boiling point
thereof under normal pressure to cause a reaction of the barium
hydroxide with the hydrous titanium oxide to provide an aqueous
slurry of barium titanate precursor; and
[0010] subjecting the barium titanate precursor thus obtained to
hydrothermal treatment over a period of not less than 24 hours to
provide barium titanate particles.
[0011] A particularly preferable method for producing barium
titanate powder according to the invention comprises the steps
of:
[0012] adding an aqueous solution of titanium tetrachloride and an
aqueous solution of an alkali at the same time to water maintained
at a temperature of 45.degree. C. to 65.degree. C. while
maintaining the temperature of the resulting reaction mixture in
the range of 45.degree. C. to 65.degree. C. and maintaining the pH
thereof in the range of 1.5 to 3.5 to simultaneously neutralize the
titanium tetrachloride with the alkali thereby to provide an
aqueous slurry of anatase hydrous titanium oxide having a BET
specific surface area in the range of 200 m.sup.2/g to 400
m.sup.2/g and a half width of diffraction peak of (101) plane in
the range of 2.3.degree. to 5.0.degree. as measured by X-ray
diffraction;
[0013] adding the aqueous slurry of anatase hydrous titanium oxide
thus obtained to an aqueous solution of barium hydroxide while
maintaining the aqueous solution of barium hydroxide at a
temperature in the range from 80.degree. C. to the boiling point
thereof under normal pressure to cause a reaction of the barium
hydroxide with the hydrous titanium oxide to provide an aqueous
slurry of barium titanate precursor; and
[0014] subjecting the barium titanate precursor thus obtained to
hydrothermal treatment over a period of not less than 24 hours to
provide barium titanate particles.
[0015] According to the invention, it is preferred that in the step
of hydrothermal treatment mentioned above, that is, in the step of
hydrothermally treating the barium titanate precursor to provide
barium titanate particles, the hydrothermal treatment temperature
is 250.degree. C. or less.
Advantageous Effects of Invention
[0016] According to the method of the invention, there is obtained
barium titanate powder which is comprised of uniform fine particles
high in tetragonality and superior in dispersibility.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a scanning electron photomicrograph (50000
magnifications) of an example of barium titanate obtained by the
method of the invention.
DESCRIPTION OF EMBODIMENTS
[0018] The method for producing barium titanate powder of the
invention comprises the steps of:
[0019] adding an aqueous slurry of anatase hydrous titanium oxide
having a BET specific surface area in the range of 200 m.sup.2/g to
400 m.sup.2/g and a half width of diffraction peak of (101) plane
in the range of 2.3.degree. to 5.0.degree. as measured by X-ray
diffraction to an aqueous solution of barium hydroxide while
maintaining the aqueous solution of barium hydroxide at a
temperature in the range from 80.degree. C. to the boiling point
thereof under normal pressure to cause a reaction of the barium
hydroxide with the hydrous titanium oxide to provide an aqueous
slurry of barium titanate precursor; and
[0020] subjecting the barium titanate precursor thus obtained to
hydrothermal treatment over a period of not less than 24 hours to
provide barium titanate particles.
[0021] When the BET specific surface area of the anatase hydrous
titanium oxide used is larger than 400 m.sup.2/g, the resulting
barium titanate is inferior in tetragonality. When the BET specific
surface area of the anatase hydrous titanium oxide used is smaller
than 200 m.sup.2/g, the anatase hydrous titanium oxide has a high
crystallinity, but on the other hand, it has a poor reactivity with
barium hydroxide with the consequence that the barium titanate
particles obtained are inferior in tetragonality.
[0022] In particular, according to the invention, the anatase
hydrous titanium oxide used has a BET specific surface area
preferably in the range of 200 m.sup.2/g to 350 m.sup.2/g, and more
preferably in the range of 220 m.sup.2/g to 330 m.sup.2/g.
[0023] Further, when the anatase hydrous titanium oxide used has a
half width of diffraction peak of (101) plane smaller than
2.3.degree. as measured by X-ray diffraction, it has a high
crystallinity, but has a poor reactivity with barium hydroxide, and
therefore the resulting barium titanate particles are low in
tetragonality. On the other hand, when the anatase hydrous titanium
oxide used has a half width larger than 5.0.degree., the resulting
barium titanate particles are low in tetragonality.
[0024] In particular, the anatase hydrous titanium oxide used in
the invention has a half width of diffraction peak of (101) plane
preferably in the range of 2.3.degree. to 4.0.degree. as measured
by X-ray diffraction, and more preferably in the range of
2.3.degree. to 3.5.degree..
[0025] As described above, the aqueous slurry of anatase hydrous
titanium oxide having a BET specific surface area in the range of
200 m.sup.2/g to 400 m.sup.2/g and a half width of diffraction peak
of (101) plane in the range of 2.3.degree. to 5.0.degree. as
measured by X-ray diffraction is obtained preferably by adding an
aqueous solution of titanium tetrachloride and an aqueous solution
of an alkali each maintained at a temperature in the range of
45.degree. C. to 65.degree. C. at the same time to water maintained
at a temperature of 45.degree. C. to 65.degree. C. beforehand to
simultaneously neutralize the titanium tetrachloride with the
alkali while maintaining the pH of the resulting reaction mixture
in the range of 1.5 to 3.5, preferably in the range of 2.0 to
3.5.
[0026] Therefore, according to the invention, the most preferred
method for producing barium titanate powder comprises the steps
of:
[0027] adding an aqueous solution of titanium tetrachloride and an
aqueous solution of an alkali at the same time to water maintained
at a temperature of 45.degree. C. to 65.degree. C. while
maintaining the temperature of the resulting reaction mixture in
the range of 45.degree. C. to 65.degree. C. and maintaining the pH
thereof in the range of 1.5 to 3.5 to simultaneously neutralize the
titanium tetrachloride with the alkali thereby to provide an
aqueous slurry of anatase hydrous titanium oxide having a BET
specific surface area in the range of 200 m.sup.2/g to 400
m.sup.2/g and a half width of diffraction peak of (101) plane in
the range of 2.3.degree. to 5.0.degree. as measured by X-ray
diffraction;
[0028] adding the aqueous slurry of anatase hydrous titanium oxide
thus obtained to an aqueous solution of barium hydroxide while
maintaining the aqueous solution of barium hydroxide at a
temperature in the range from 80.degree. C. to the boiling point
thereof under normal pressure to cause a reaction of the barium
hydroxide with the hydrous titanium oxide to provide an aqueous
slurry of barium titanate precursor; and
[0029] subjecting the barium titanate precursor thus obtained to
hydrothermal treatment over a period of not less than 24 hours to
provide barium titanate particles.
[0030] According to the invention, as described above, the aqueous
slurry of anatase hydrous titanium oxide is obtained preferably by
simultaneously neutralizing titanium tetrachloride with an alkali.
Herein, the simultaneous neutralization of the titanium
tetrachloride with the alkali refers to simultaneously adding an
aqueous solution of titanium tetrachloride and an aqueous solution
of alkali into a container containing water and mixing them in the
container to neutralize the titanium tetrachloride with the
alkali.
[0031] In the simultaneous neutralization of the titanium
tetrachloride with the alkali described above, the concentration of
the hydrous titanium oxide in the slurry when the simultaneous
neutralization has been completed is not particularly limited, and
it is usually preferred that it is in the range of 10 g/L to 50 g/L
in terms of TiO.sub.2. In case that the concentration of the
hydrous titanium oxide in the slurry is higher than 50 g/L in terms
of TiO.sub.2 when the simultaneous neutralization has been
completed, amorphous hydrous titanium oxide is likely to generate,
and therefore it becomes difficult to obtain anatase hydrous
titanium oxide. On the other hand, in case that the concentration
of the hydrous titanium oxide in the slurry is lower than 10 g/L in
terms of TiO.sub.2 when the simultaneous neutralization has been
completed, the productivity is likely to be poor.
[0032] Further, in the simultaneous neutralization of the titanium
tetrachloride with the alkali described above, the temperatures of
water, the aqueous solution of titanium tetrachloride, and the
aqueous solution of the alkali do not need to be all the same, but
the temperatures are preferably close to each other, most
preferably all the same, in particular.
[0033] As the aqueous solution of the alkali solution, an aqueous
solution of an alkali metal hydroxide such as sodium hydroxide and
potassium hydroxide, ammonia, and the like are preferably used. In
place of the aqueous solution of alkali, a solid alkali compound
may be directly added.
[0034] Even if the pH of the resulting reaction mixture is in the
range of 1.5 to 3.5 in the simultaneous neutralization of the
titanium tetrachloride with the alkali described above, when the
neutralization temperature is lower than 45.degree. C., the anatase
hydrous titanium oxide cannot be obtained, and the BET specific
surface area of the resulting hydrous titanium oxide exceeds 400
m.sup.2/g.
[0035] When the neutralization temperature is higher than
65.degree. C., the titanium tetrachloride is hydrolyzed, and rutile
hydrous titanium oxide is likely to generate or the half width of
the hydrous titanium oxide becomes smaller than 2.3.degree.. The
rutile hydrous titanium oxide has a poor reactivity with barium
hydroxide and the barium titanate particles obtained are inferior
in tetragonality. Also when the half width of the hydrous titanium
oxide is smaller than 2.3.degree., the barium titanate particles
obtained are inferior in tetragonality.
[0036] On the other hand, even if the neutralization temperature is
in the range of 45.degree. C. to 65.degree. C., when the pH of the
resulting reaction mixture is higher than 3.5, the anatase hydrous
titanium oxide cannot be obtained and the BET specific surface area
of the resulting hydrous titanium oxide exceeds 400 m.sup.2/g. When
using such hydrous titanium oxide, the barium titanate particles
obtained are inferior in tetragonality.
[0037] When the pH of the resulting reaction mixture is lower than
1.5, a large amount of chloride ions remain as impurities in the
hydrous titanium oxide produced, and as a result, the reactivity
thereof with barium hydroxide deteriorates and thus the barium
titanate particles obtained are inferior in tetragonality.
[0038] Thus, according to the invention, titanium tetrachloride is
simultaneously neutralized with the alkali in water to provide
hydrous titanium oxide, the resulting slurry is filtered and washed
with water to remove therefrom the chloride ions and the like
generated in the neutralization, and the resulting cake is
dispersed in water, thereby the aqueous slurry of hydrous titanium
oxide is obtained which can be preferably used in the step of
obtaining an aqueous slurry of the barium titanate precursor.
[0039] The aqueous slurry of anatase hydrous titanium oxide having
a BET specific surface area in the range of 200 m.sup.2/g to 400
m.sup.2/g and a half width of diffraction peak of (101) plane in
the range of 2.3.degree. to 5.0.degree. as measured by X-ray
diffraction is added to an aqueous solution of barium hydroxide
while maintaining the aqueous solution of barium hydroxide at a
temperature in the range from 80.degree. C. to the boiling point
thereof under normal pressure to cause a reaction of the barium
hydroxide with the hydrous titanium oxide as described above to
provide an aqueous slurry of barium titanate precursor.
[0040] The barium titanate precursor obtained by the reaction of
the barium hydroxide with the hydrous titanium oxide is usually
comprised of fine particles of barium titanate having a BET
specific surface area in the range of 50 m.sup.2/g to 200
m.sup.2/g. Since the reaction between the barium hydroxide and the
hydrous titanium oxide is a reaction under normal pressure, the
barium titanate precursor obtained has a Ba/Ti ratio smaller than
1, but it has been confirmed by powder X-ray diffraction that the
barium titanate precursor obtained has a crystal structure of
barium titanate.
[0041] In the aqueous solution of barium hydroxide, the solvent may
contain a water-soluble organic solvent insofar as the reaction of
the barium hydroxide with the hydrous titanium oxide is not
adversely affected. As such a water-soluble organic solvent,
ethylene glycol, diethylene glycol, polyethylene glycol, and the
like can be mentioned, for example.
[0042] When obtaining the barium titanate precursor by the reaction
of the barium hydroxide with the hydrous titanium oxide, it is
preferred that the barium hydroxide and the hydrous titanium oxide
are used in such a manner that the Ba/Ti molar ratio is in the
range of 1.1 to 3.0 when the addition of the aqueous slurry of
anatase hydrous titanium oxide to the aqueous barium hydroxide
solution has been completed. In the reaction of the barium
hydroxide with the hydrous titanium oxide, when the Ba/Ti molar
ratio is smaller than 1.1, the alkalinity of the resulting reaction
system is low so that the reactivity between the barium hydroxide
and the hydrous titanium oxide deteriorates. When the Ba/Ti molar
ratio is higher than 3.0, the reactivity between the barium
hydroxide and the hydrous titanium oxide has no problems; however,
since the barium hydroxide which does not contribute to the
reaction is excessively used, there is caused a problem that the
production cost becomes high.
[0043] In the step of obtaining the aqueous slurry of the barium
titanate precursor described above, the temperature at which the
barium hydroxide is reacted with the hydrous titanium oxide is
important. Even if the anatase hydrous titanium oxide has a BET
specific surface area in the range of 200 m.sup.2/g to 400
m.sup.2/g and a half width in the range of 2.3.degree. to
5.0.degree. as described above, when the temperature of the
reaction thereof with the barium hydroxide is lower than 80.degree.
C. under normal pressure, barium titanate particles with a high
tetragonality cannot be obtained. The upper limit of the reaction
temperature is a temperature up to the boiling point of the
reaction mixture containing the barium hydroxide.
[0044] According to the method of the invention, the barium
titanate precursor obtained as described above is subjected to
hydrothermal treatment over a period of not less than 24 hours, the
resulting slurry is filtered, washed with water, and then dried, to
provide the intended barium titanate powder comprised of uniform
fine particles superior in tetragonality. If it is intended to
synthesize barium titanate only by the hydrothermal treatment
without passing through the barium titanate precursor, the reaction
of the barium hydroxide with hydrous titanium oxide progresses
simultaneously with the particle growth of the resulting barium
titanate particles, and, as a result, a large amount of hydroxyl
groups are taken into the barium titanate particles, which makes it
difficult to obtain barium titanate particles with a high
tetragonality.
[0045] The aqueous slurry of the barium titanate precursor
subjected to hydrothermal treatment preferably contains the barium
titanate precursor in a concentration in the range of 0.4 mol/L to
1.0 mol/L in terms of BaTiO.sub.3.
[0046] The aqueous slurry of the barium titanate precursor may be
subjected to the hydrothermal treatment while maintaining the
obtained concentration without condensing or diluting the same.
[0047] The aqueous slurry of the barium titanate precursor is put
into an autoclave usually as it is, and is then subjected to the
hydrothermal treatment at a temperature that exceeds the boiling
point thereof under normal pressure and that is usually not more
than 250.degree. C., preferably in the range of 105.degree. C. to
250.degree. C.
[0048] In the method of the invention, the hydrothermal treatment
is performed over a period of 24 hours or more, usually in the
range of 24-1000 hours, preferably in the range of 24-500 hours,
and most preferably in the range of 24-200 hours. According to the
invention, the particle diameter of barium titanate obtained can be
controlled by the temperature at which and time for which the
hydrothermal treatment is performed.
[0049] That is, the particle diameter of the barium titanate
increases with increasing temperature at which the hydrothermal
treatment is performed, while the particle diameter of the barium
titanate increases with increasing time for which the hydrothermal
treatment is performed. In particular, according to the present
invention, there is obtained barium titanate larger in particle
diameter and higher in tetragonality by performing the hydrothermal
treatment for a longer time of period. When the hydrothermal
treatment is performed for a period of shorter than 24 hours, the
resulting particles of barium titanate do not grow sufficiently to
be low in tetragonality.
[0050] After the aqueous slurry of the barium titanate precursor
has been hydrothermally treated in this way, the content in the
autoclave is cooled to normal temperature, the obtained slurry is
filtered, washed with water, and then dried to obtain barium
titanate powder. The drying temperature is usually in the range of
100.degree. C. to 150.degree. C.
[0051] The barium titanate powder thus obtained is comprised of
uniform fine particles superior in tetragonality, and it usually
has a BET specific surface area in the range of 3 m.sup.2/g to 70
m.sup.2/g, preferably in the range of 4 m.sup.2/g to 20
m.sup.2/g.
[0052] In the invention, the tetragonality of the barium titanate
is evaluated on the basis of c/a ratio, which can be determined
from powder X-ray diffraction of the barium titanate powder. The
barium titanate powder obtained according to the invention has a
c/a ratios of 1.008 or more, the tetragonality in that sense. Thus,
the barium titanate powder obtained is superior in
tetragonality.
[0053] As set forth above, because the barium titanate obtained in
this way has a high tetragonality only by the hydrothermal
treatment of barium titanate precursor, there is no need for the
barium titanate obtained to be further calcined and
disintegrated.
[0054] As described above, the particles of barium titanate
obtained by the invention are high in tetragonality and superior in
dispersibility. Further, the particles of barium titanate high in
tetragonality are also high in dielectricity, and therefore is
suitably used as a material for dielectrics. As a consequence, the
barium titanate powder obtained by the invention can be suitably
used as a dielectric material to meet the demand of reducing the
layers thickness in the manufacturing of the MLCC.
[0055] The invention is described in detail with reference to
Examples, but the present invention is not limited to Examples.
EXAMPLES
Example 1
Preparation of Aqueous Slurry of Hydrous Titanium Oxide
[0056] 500 mL of pure water was put into a beaker and then warmed
to 55.degree. C. 350 mL of an aqueous solution of titanium
tetrachloride (manufactured by Osaka Titanium Technologies Co.,
Ltd., 3.8 mol/L in terms of TiO.sub.2) and 7 L of pure water were
added at the same time to the water at a rate of 2.5 mL/minute and
50 mL/minute, respectively, while simultaneously an aqueous sodium
hydroxide solution having a concentration of 30% by weight was also
added to the water, and while maintaining the resulting mixture at
a pH of 2.5 and at a temperature of 55.degree. C., to
simultaneously neutralize the titanium tetrachloride with the
alkali, the sodium hydroxide, thereby an aqueous slurry of hydrous
titanium oxide having a concentration of 14 g/L in terms of
TiO.sub.2 was obtained.
[0057] The aqueous slurry thus obtained was filtered and then
washed with water to remove sodium ions and chloride ions
therefrom. Pure water was added to the obtained cake to provide an
aqueous slurry of anatase hydrous titanium oxide having a
concentration of 110 g/L in terms of TiO.sub.2.
(Preparation of Aqueous Slurry of Barium Titanate Precursor)
[0058] 567 mL of pure water and 959 g of barium hydroxide
octahydrate (manufactured by Sakai Chemical Industry Co., Ltd.)
were put into a 5 L-capacity reaction vessel, and then heated to
100.degree. C. to dissolve the barium hydroxide octahydrate in
water to prepare an aqueous barium hydroxide solution.
[0059] The aqueous slurry of the hydrous titanium oxide was added
while maintaining the temperature at 100.degree. C. to the aqueous
solution of barium hydroxide while maintaining the temperature at
100.degree. C. in 1 hour, and they were reacted at a temperature of
100.degree. C. for 2 hours, thereby an aqueous slurry of barium
titanate precursor having a concentration of 0.66 mol/L in terms of
BaTiO.sub.3 was obtained. The Ba/Ti molar ratio in the resulting
reaction mixture was 2.3 when the addition of the aqueous slurry of
hydrous titanium oxide to the aqueous barium hydroxide solution was
completed.
(Hydrothermal Treatment of Aqueous Slurry of Barium Titanate
Precursor)
[0060] The aqueous slurry of the barium titanate precursor having a
concentration of 0.66 mol/L in terms of BaTiO.sub.3 obtained above
was placed in an autoclave vessel, and then subjected to
hydrothermal treatment at 180.degree. C. for 120 hours. Then, the
content in the autoclave was allowed to cool to room temperature.
The obtained aqueous slurry was filtered, washed with water, and
then dried at 130.degree. C. to give barium titanate powder.
[0061] FIG. 1 is a scanning electron microphotograph (50000
magnifications) of barium titanate powder obtained above. The
invention provides barium titanate powder comprised of uniform fine
particles.
Example 2
[0062] Barium titanate powder was obtained in the same manner as in
Example 1 except that the aqueous slurry of the barium titanate
precursor was hydrothermally treated at a temperature of
180.degree. C. for 48 hours.
Example 3
[0063] Barium titanate powder was obtained in the same manner as in
Example 1 except that the aqueous slurry of the barium titanate
precursor was hydrothermally treated at a temperature of
200.degree. C. for 24 hours.
Example 4
[0064] Barium titanate powder was obtained in the same manner as in
Example 1 except that the aqueous slurry of the barium titanate
precursor was hydrothermally treated at a temperature of
160.degree. C. for 168 hours.
Example 5
[0065] Barium titanate powder was obtained in the same manner as in
Example 1 except that the aqueous slurry of the barium titanate
precursor was hydrothermally treated at a temperature of
200.degree. C. for 180 hours.
Example 6
[0066] Barium titanate powder was obtained in the same manner as in
Example 1 except that the simultaneous neutralization of titanium
tetrachloride was performed at a pH of 3.5 and at a temperature of
45.degree. C., and the hydrothermal treatment of barium titanate
precursor was performed at a temperature of 170.degree. C. for 96
hours.
Example 7
[0067] Barium titanate powder was obtained in the same manner as in
Example 1 except that the simultaneous neutralization of titanium
tetrachloride was performed at a pH of 2.0 and at a temperature of
45.degree. C., and the hydrothermal treatment of barium titanate
precursor was performed at a temperature of 200.degree. C. for 24
hours.
Comparative Example 1
Preparation of Aqueous Slurry of Hydrous Titanium Oxide
[0068] 500 mL of pure water was put into a beaker, and was
maintained at a temperature of 60.degree. C. 350 mL of an aqueous
solution of titanium tetrachloride (manufactured by Osaka Titanium
Technologies Co., Ltd., 3.8 mol/L in terms of TiO.sub.2) and 7 L of
pure water were added at the same time to the water at a rate of
2.5 mL per minute and 50 mL per minute, respectively, while
simultaneously an aqueous solution of sodium hydroxide having a
concentration of 30% by weight was added to the water and while
simultaneously the resulting mixture was adjusted at a pH of 2.0
and at a temperature of 60.degree. C., to simultaneously neutralize
the titanium tetrachloride, thereby an aqueous slurry of hydrous
titanium oxide having a concentration of 14 g/L in terms of
TiO.sub.2 was obtained.
[0069] The aqueous slurry was filtered and then washed with water
to remove sodium ions and chloride ions therefrom. Pure water was
added to the obtained cake to provide an aqueous slurry of anatase
hydrous titanium oxide having a concentration of 110 g/L in terms
of TiO.sub.2.
(Preparation of Aqueous Slurry of Barium Titanate Precursor)
[0070] 567 mL of pure water and 959 g of barium hydroxide
octahydrate (manufactured by Sakai Chemical Industry Co., Ltd.)
were put into a 5 L-capacity reaction vessel, and then heated to
100.degree. C. to dissolve the barium hydroxide octahydrate in
water to prepare an aqueous barium hydroxide solution.
[0071] The aqueous slurry of the hydrous titanium oxide was added
while maintaining the temperature at 100.degree. C. to the aqueous
solution of barium hydroxide while maintaining the temperature at
100.degree. C. in 1 hour, and they were reacted at a temperature of
100.degree. C. for 2 hours, thereby an aqueous slurry of barium
titanate precursor having a concentration of 0.66 mol/L in terms of
BaTiO.sub.3 was obtained. The Ba/Ti molar ratio in the resulting
reaction mixture was 2.3 when the addition of the aqueous slurry of
hydrous titanium oxide to the aqueous barium hydroxide solution was
completed.
(Hydrothermal Treatment of Aqueous Slurry of Barium Titanate
Precursor)
[0072] The aqueous slurry of the barium titanate precursor having a
concentration of 0.66 mol/L in terms of BaTiO.sub.3 obtained above
was placed in an autoclave vessel, and then subjected to
hydrothermal treatment at 190.degree. C. for 0.5 hours. Then, the
content in the autoclave was allowed to cool to room temperature.
The obtained aqueous slurry was filtered, washed with water, and
then dried at 130.degree. C. to give barium titanate powder.
Comparative Example 2
[0073] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a temperature of
50.degree. C., and the hydrothermal treatment of barium titanate
precursor was performed at a temperature of 180.degree. C. for 20
hours.
Comparative Example 3
[0074] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a temperature of
50.degree. C., and the hydrothermal treatment of barium titanate
precursor was performed at a temperature of 205.degree. C. for 2
hours.
Comparative Example 4
[0075] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a pH of 3.0, reaction of
hydrous titanium oxide and barium hydroxide was performed at a
temperature of 100.degree. C. for 5 hours, and the hydrothermal
treatment of barium titanate precursor was performed at a
temperature of 130.degree. C. for 0.5 hours.
Comparative Example 5
[0076] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a temperature of
50.degree. C., the reaction of hydrous titanium oxide and barium
hydroxide was performed at a temperature of 80.degree. C. for 5
hours, and the hydrothermal treatment of barium titanate precursor
was performed at a temperature of 200.degree. C. for 2 hours.
Comparative Example 6
[0077] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a pH of 3.0, the
reaction of hydrous titanium oxide and barium hydroxide was
performed at a temperature of 95.degree. C. for 5 hours, and the
hydrothermal treatment of barium titanate precursor was performed
at a temperature of 180.degree. C. for 0.5 hours.
Comparative Example 7
[0078] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a temperature of
50.degree. C., the reaction of hydrous titanium oxide and barium
hydroxide was performed at a temperature of 100.degree. C. for 2
hours, and the hydrothermal treatment of barium titanate precursor
was performed at a temperature of 110.degree. C. for 2 hours.
Comparative Example 8
[0079] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a pH of 5.0 and at a
temperature of 20.degree. C., the reaction of hydrous titanium
oxide and barium hydroxide was performed at a temperature of
70.degree. C. for 2 hours, and the hydrothermal treatment of barium
titanate precursor was performed at a temperature of 150.degree. C.
for 160 hours.
Comparative Example 9
[0080] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a pH of 2.5 and at a
temperature of 55.degree. C., and the hydrothermal treatment of
barium titanate precursor was performed at a temperature of
250.degree. C. for 2 hours.
Comparative Example 10
[0081] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a temperature of
45.degree. C., and the hydrothermal treatment of barium titanate
precursor was performed at a temperature of 180.degree. C. for 20
hours.
Comparative Example 11
[0082] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a temperature of
80.degree. C., and the hydrothermal treatment of barium titanate
precursor was performed at a temperature of 200.degree. C. for 24
hours.
Comparative Example 12
[0083] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a pH of 1.5 and at a
temperature of 20.degree. C., and the hydrothermal treatment of
barium titanate precursor was performed at a temperature of
160.degree. C. for 40 hours.
Comparative Example 13
[0084] Barium titanate powder was obtained in the same manner as in
Comparative Example 1 except that the simultaneous neutralization
of titanium tetrachloride was performed at a pH of 4.0 and at a
temperature of 40.degree. C., and the hydrothermal treatment of
barium titanate precursor was performed at a temperature of
170.degree. C. for 24 hours.
[0085] The reaction conditions in the above-described Examples 1-7
and Comparative Examples 1-13, i.e., the pH and temperature at
which titanium tetrachloride was simultaneously neutralized with
sodium hydroxide, the reaction temperature at which and the
reaction time for which the hydrous titanium oxide was reacted with
barium hydroxide to provide the barium titanate precursor, and the
temperature at which and the time for which the aqueous slurry of
barium titanate precursor was hydrothermally treated are shown in
Table 1.
[0086] The properties of the hydrous titanium oxide used in
Examples 1-7 and Comparative Examples 1-13, and the properties of
the barium titanate powder obtained in Examples 1-7 and Comparative
Examples 1-13 are shown in Table 2.
(Crystal Structure of Hydrous Titanium Oxide)
[0087] A small amount of the aqueous slurry of hydrous titanium
oxide obtained by simultaneously neutralizing titanium
tetrachloride with sodium hydroxide was withdrawn, filtered and
washed with water, and dried to provide powder. The crystal
structure of the powder was examined using a powder X-ray
diffraction apparatus (RINT-TTR III, manufactured by Rigaku
Corporation, Radiation source: CuK.alpha.).
[0088] Further, the half width was calculated from the peak of
(101) plane and was used as the index of the crystallinity of the
hydrous titanium oxide. As shown in Table 2, the peak of the
hydrous titanium oxide in each of Comparative Examples 8, 12 and 13
was found to be very broad, and thus the hydrous titanium oxides
obtained therein were judged to be amorphous.
(c/a Ratio of Barium Titanate)
[0089] The barium titanate powder was subjected to powder X-ray
diffraction using a powder X-ray diffraction apparatus (RINT-TTR
III, manufactured by Rigaku Corporation, Radiation source:
CuK.alpha.), and then the c/a ratio was determined using the WPPF
method.
(Specific Surface Areas of Hydrous Titanium Oxide Powder and Barium
Titanate Powder)
[0090] The specific surface area of each of the hydrous titanium
oxide powder and the barium titanate powder was measured by a
single point BET method using a fully automatic specific surface
area meter (HM Model-1220, manufactured by Mountech Co., Ltd.),
after degassing at 205.degree. C. for 30 minutes.
TABLE-US-00001 TABLE 1 Preparation of Preparation of Hydrothermal
Hydrous Barium Titanate Treatment Titanium Oxide Precursor
Temperature Temper- Temper- Temper- ature ature Time ature Time pH
(.degree. C.) (.degree. C.) (h) (.degree. C.) (h) Example 1 2.5 55
100 2.0 180 120 Example 2 2.5 55 100 2.0 180 48 Example 3 2.5 55
100 2.0 200 24 Example 4 2.5 55 100 2.0 160 168 Example 5 2.5 55
100 2.0 200 180 Example 6 3.5 45 100 2.0 170 96 Example 7 2.0 45
100 2.0 200 24 Comparative 1 2.0 60 100 2.0 190 0.5 Comparative 2
2.0 50 100 2.0 180 20 Comparative 3 2.0 50 100 2.0 205 2.0
Comparative 4 3.0 60 100 5.0 130 0.5 Comparative 5 2.0 50 80 5.0
200 2.0 Comparative 6 3.0 60 95 5.0 180 0.5 Comparative 7 2.0 50
100 2.0 110 2.0 Comparative 8 5.0 20 70 2.0 150 160 Comparative 9
2.5 55 100 2.0 250 2.0 Comparative 10 2.0 45 100 2.0 180 20
Comparative 11 2.0 80 100 2.0 200 24 Comparative 12 1.5 20 100 2.0
160 40 Comparative 13 4.0 40 100 2.0 170 24
TABLE-US-00002 TABLE 2 Hydrous Titanium Oxide Barium Titanate
Specific Specific Surface Half Surface Area Crystal Width Area
(m.sup.2/g) Structure*.sup.) (Degrees) (m.sup.2/g) c/a Example 1
255 A 2.5 7.4 1.010 Example 2 255 A 2.5 10.5 1.008 Example 3 249 A
2.4 11.7 1.008 Example 4 249 A 2.4 10.1 1.009 Example 5 255 A 2.5
4.9 1.010 Example 6 322 A 3.1 8.7 1.008 Example 7 284 A 3.0 8.6
1.008 Comparative 1 270 A 2.5 20.6 1.006 Comparative 2 256 A 2.5
11.8 1.007 Comparative 3 256 A 2.5 17.1 1.006 Comparative 4 226 A
2.4 48.3 1.005 Comparative 5 256 A 2.5 21.7 1.006 Comparative 6 226
A 2.4 25.2 1.006 Comparative 7 256 A 2.5 68.4 1.003 Comparative 8
409 Am 6.3 8.1 1.007 Comparative 9 255 A 2.5 17.0 1.006 Comparative
10 284 A 3.0 13.7 1.007 Comparative 11 158 A 1.6 10.2 1.007
Comparative 12 401 Am 5.5 15.9 1.006 Comparative 13 422 Am 6.5 14.7
1.006 *.sup.)A represents "anatase"; Am represents "amorphous".
[0091] As shown in Table 2, the barium titanate powder obtained by
the method of the invention has a specific surface area in the
range of 4 to 20 m.sup.2/g and a c/a ratio of 1.008 or more. Thus,
the barium titanate powder obtained by the method of the invention
is comprised of fine particles superior in tetragonality.
[0092] Further, the method of the invention needs no calcination of
barium titanate powder obtained by hydrothermal treatment of barium
titanate precursor, and accordingly the method of the invention
usually provides barium titanate powder superior in dispersibility
without disintegration of the resulting barium titanate powder.
* * * * *